Plasma for patterning advanced gate stacks

ABSTRACT

A plasma composition and its use in a method for the dry etching of a stack of at least one material chemically too reactive towards the use of a Cl-based plasma are provided. Small amounts of nitrogen (5% up to 10%) can be added to a BCl 3  comprising plasma and used in an anisotropical dry etching method whereby a passivation film is deposited onto the vertical sidewalls of stack etched for protecting the vertical sidewalls from lateral attack such that straight profiles can be obtained.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.provisional application Ser. No. 60/731,608, filed Oct. 28, 2005, andU.S. provisional application Ser. No. 60/839,897, filed Aug. 23, 2006,the disclosures of which are hereby expressly incorporated by referencein their entirety and are hereby expressly made a portion of thisapplication.

FIELD OF THE INVENTION

A method of dry etching of advanced gate stacks is provided which can beused to etch metal gate comprising stacks and pure germanium comprisingstacks. An etch plasma composition is also provided for dry etching ofmetal gate comprising stacks and pure germanium comprising stacks,thereby preserving the vertical profile of the gate stack afterpatterning.

BACKGROUND OF THE INVENTION

As the critical dimensions in CMOS manufacturing shrink for the 90 nmtechnology node and beyond, conventional (poly) silicon gates are beingreplaced by metal gates (meaning pure metals, metal alloys or metalnitrides, etc) and SiO₂ as a gate dielectric is replaced by materialswith higher dielectric constant (so called “high-k dielectrics). The keychallenge is to adapt the conventional gate etch process flow to themetal gate stack. Etching this metal gate stack now requires a processthat defines the metal gate profile without affecting the gate criticaldimension (CD) and stops on thin gate oxide without pitting or punchthrough.

Etching of metal gates has been studied addressing metal gate and gateoxide surface roughness, CD control, etch selectivity, and low damageetching but none of them succeeded in preserving the vertical profile ofthe gate stack after patterning.

One of the promising chemistry for patterning of advanced gate stacks(metal gate etch or high-k removal) is BCl₃. The main advantage of thisplasma is that it can etch both metal gates and high-k dielectric withreasonable selectivity to the Si substrate. However, there are number ofgate stack materials that are incompatible with BCl₃ plasma as they aretoo reactive. As a result, BCl₃ produces some undesirable lateral etchthat compromises the gate profiles. Two particular examples are Ge gatesand TaN metal gates. If a pure BCl₃ plasma is applied during thepatterning of the gate stacks containing Ge or TaN a profile distortioncaused by lateral etch is observed.

SUMMARY OF THE INVENTION

A dry-etch plasma composition for preserving the vertical profile of astructure comprising a stack of layers during anisotropical dry-etchpatterning is provided.

Said plasma composition is further characterized such that during thedry-etch patterning of said stack a water-soluble film, which isremovable against the structure, is deposited onto the sidewalls of saidstack such that lateral attack of said patterned stack is avoided.

Preferably, the plasma composition of preferred embodiments ischaracterized as a plasma comprising a boron-halogen compound andnitrogen and wherein the ratio of the boron-halogen compound to nitrogenis from 19:1 up to 9:1. More preferred, the plasma composition of thepreferred embodiments is characterized as a plasma composition whereinsaid plasma comprises a boron-halogen compound, nitrogen and optionallyan inert compound. Most preferred said boron-halogen compound is BCl₃.

Preferably, the plasma composition of the preferred embodiments ischaracterized as a plasma comprising (or consisting of) a boron-halogencompound and 5 up to 10% nitrogen (of the total plasma composition).

More preferably, the plasma composition comprises (or consists of) aboron-halogen compound and less than 10% nitrogen (of the total plasmacomposition). More particularly, said boron-halogen compound is BCl₃.

Most preferred, said plasma is (i.e. consists of) a BCl₃ plasma furthercomprising (or to which is added) from 5% to 10% nitrogen (based on thetotal plasma composition).

In a preferred embodiment, the stack of layers to be patterned is ametal gate comprising stack.

More preferred, said metal gate comprising stack comprises at least oneTaN layer or combinations of a TaN layer and a TiN layer (referred to asTaN/TiN metal gates) wherein said TaN layer is too sensitive to a (pure)BCl₃ plasma. Or in other words the stack of layers to be patterned is astack wherein at least one layer of said stack of layers is a TaN layer.

In another preferred embodiment, at least one layer of said stack oflayers to be patterned is a germanium comprising layer.

Said germanium layer can be situated upon a layer to be patterned by theplasma composition. Said germanium layer can be a pure Ge layer.

Preferably, the plasma of the preferred embodiments (during patterning)has a substrate bias which is different from zero.

Preferably, the plasma of the preferred embodiments (during patterning)has a plasma power of from 100 W up to 1200 W. More preferred saidplasma power is about 450 W.

Preferably, the plasma of the preferred embodiments (during patterning)has a pressure in the plasma chamber of minimum 0.666 Pa (5 mT) andmaximum 10.665 Pa (80 mT). More preferred said pressure is 0.666 Pa (5mT).

Preferably, the plasma of the preferred embodiments (during patterning)has a temperature below 100° C. and most preferred said plasmatemperature during dry-etch patterning is about 60° C.

An anisotropical dry etching method is also provided using the plasmacomposition of the preferred embodiments as described above forpatterning a stack of layers to create a vertical structure whereinlateral attack during patterning of said stack is avoided.

Preferably said method comprises the steps of first applying a dry-etchstep using the plasma composition of the preferred embodiments whereinduring the etching a protective and water-soluble film is deposited ontothe vertical sidewalls of said structure such that the vertical profileof said structure is preserved and lateral attack is avoided. In a nextstep said water-soluble film is removed from said structure.

Said water-soluble film is preferably removed using a wet removalprocess using water.

Use is provided of a plasma comprising (or consisting of) BCl₃, to whichnitrogen is added to reach 5% to 10% of the total volume of theresulting plasma composition, for etching a (suitable) stack of layer(i.e. comprising at least one layer etchable by said BCl₃ component) andsimultaneously passivating (or protecting) the sidewalls of said stackof layers from lateral etch.

A method is also provided for etching (or patterning) a (suitable) stackof layers while/and simultaneously passivating (or protecting) thesidewalls of said stack of layers comprising the step of providing aplasma comprising (or consisting of) BCl₃, to which nitrogen is added toreach 5% to 10% of the total volume of the resulting plasma composition.

Said use or said method is particularly useful for (patterning) a stackof layers wherein at least one layer is germanium, or at least one layeris TaN.

Said passivating (or protecting) effect results from the formation anddeposition of a film (or layer) which contains boron and nitrogen (andfurther compounds such as oxygen) on the sidewalls of said stack oflayers. Said film obtainable by a method of the preferred embodiments isalso provided.

Said use or said method can be carried out in the framework of CMOSmanufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

All drawings are intended to illustrate some aspects and embodiments ofthe present invention. Not all alternatives and options are shown andtherefore the invention is not limited to the content of the givendrawings.

FIG. 1 shows FTIR (Fourier Transform Infrared Spectroscopy) spectra offilms deposited from BCl₃/N₂ plasma mixture (70% BCl₃) at 275° C. and60° C.

FIG. 2 shows a Ge gate profile after the gate patterning and before thehigh-k removal.

FIG. 3 shows a Ge gate profile after high-k removal by pure BCl₃ plasmafor 10 seconds (FIG. 3A) and BCl₃/N₂ (10% N₂) plasma for 20 seconds(FIG. 3B)

FIG. 4 shows a TaN gate profile after etching in pure BCl₃ plasma (FIG.4A), an arrow indicates the lateral attack of TaN. FIG. 4B shows a TaNgate profile after etching in BCl₃/N₂ (5% N₂) plasma.

FIG. 5 shows a TaN gate profile after etching in BCl₃/N₂ plasma (FIG.5A) and a TaN gate profile after etching in BCl₃/O₂ plasma (FIG. 5B).

FIG. 6 illustrates the deposition rate of a BxNy film using aBCl₃/N₂plasma (Pressure=1,333 Pa (10 mT)).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments are illustrated in referenced figures of thedrawings. It is intended that the embodiments and figures herein are tobe considered illustrative rather than restrictive.

In the context of the preferred embodiments, the term “criticaldimension” (CD) as used herein is a broad term, and is to be given itsordinary and customary meaning to a person of ordinary skill in the art(and is not to be limited to a special or customized meaning), andrefers without limitation to the smallest dimensions of geometricalfeatures (e.g. width of gate electrode) which can be formed duringsemiconductor device manufacturing. In the context of the preferredembodiments the term “bias” as used herein is a broad term, and is to begiven its ordinary and customary meaning to a person of ordinary skillin the art (and is not to be limited to a special or customizedmeaning), and refers without limitation to the voltage applied to thesubstrate during patterning in a dry etch chamber.

The term “selectivity” as used herein is a broad term, and is to begiven its ordinary and customary meaning to a person of ordinary skillin the art (and is not to be limited to a special or customizedmeaning), and refers without limitation to the etch rate of a selectedmaterial towards another material. The material to be etched away shouldhave a much higher etch rate than the other materials.

The term “ratio” as used herein is a broad term, and is to be given itsordinary and customary meaning to a person of ordinary skill in the art(and is not to be limited to a special or customized meaning), andrefers without limitation to an expression of an amount of a firstcompound to a second compound, e.g. a ratio of 9:1 means e.g. 9 sccm(standard centimeter cube per minute) of the first compound and 1 sccmof the second compound.

Use of plasma composition according to the preferred embodimentssurprisingly results in the deposition of a BxNy film during the etchingof a structure wherein the deposition is performed in a plasma etchchamber (e.g., Versys 2300 etch chamber from LAM®) at low temperatures(e.g. 60° C.), which was never reported before (BN deposition is usuallyperformed at temperatures of 390° C.-650° C.). The BxNy film isdeposited at a rate as high as 10 nm/min to more than 100 nm/mindepending on the pressure, plasma power, gas flows, and plasmacomposition (more specifically the BCl₃ to N₂ ratio). Said depositedBxNy-like film, in contrast to a pure BN film, was found to be easilydecomposing by temperature (the film thickness decreases at temperaturesabove 100° C.) and soluble in water at room temperatures.

The preferred embodiments are further related to the patterning of astack of layers, more specifically to the dry etching of a stack oflayers.

Said patterning is making use of a plasma etch compound wherein at leastone of the layers is too sensitive to said etch compound. By adding anextra component to the plasma it is possible to deposit a protectivelayer onto the stack of layers such that said stack is protected fore.g. sidewall damage. Said protective layer is deposited during thepatterning (dry etching). Furthermore said protective layer issacrificial and hence easy removable.

The “sacrificial” layer, also referred to as “protective” layer or“passivation” layer refers to the BxNy like film resulting from theaddition of nitrogen in the boron-halogen plasma, also referred to asBxNy film or as to boron nitride like film, which is deposited duringetching. Said BxNy film is used as a “protective” or “passivating” filmduring patterning/etching of a structure, said BxNy film is alsoreferred to as a sacrificial layer because said layer is removed afterpatterning is completed. Due the unstable character of the BxNy film andwater soluble character said BxNy film can be easily removed by e.g. awater rinse.

The term “BxNy” film refers to a film comprising mainly boron andnitrogen which is further characterized as a water-soluble film. TheBxNy film of the preferred embodiments is water soluble, in contrast toa pure BN which is insoluble in water. The BxNy film contains hexagonalboron nitride, but is very unlikely to be a stoichiometric BN. The BxNyfilm is therefore referred to as BxNy wherein the integers x and yindicate that the ratio of nitrogen and boron in the film is not fixeddue to the presence of other compounds (impurities) in the film such aswater, oxygen and/or ammonia which are possibly absorbed from the plasmaand/or atmosphere after dry-etching.

More specifically, the preferred embodiments relate to the patterning ofmetal gate stacks or germanium gate stacks, more specifically it relatesto the dry etching of said gate stacks such as TaN comprising metal gatestacks and to the dry etching of Ge comprising stacks (or in other wordsa stack comprising e.g. a pure Ge layer).

The methods and compositions of preferred embodiments can solve orminimize the problem of lateral etch and profile attack during thepatterning of advanced gate stacks such as metal gate stacks andgermanium stacks by adding small amounts of nitrogen to a boron-halogenplasma such as BCl₃ plasma in order to improve gate profile control. Themixture of BCl₃/N₂ plasma results in a deposition of BxNy-like film thatinhibits the lateral etch but does not inhibit vertical etch as theformed BxNy-like film is destroyed by ion bombardment.

A plasma composition is provided for patterning metal gate stacks and/orgermanium stacks wherein during the patterning of said stack aprotective and water-soluble film is deposited such that the verticalprofile of the stack is preserved and lateral attack of said stack isavoided.

More specifically a plasma composition is provided for patterning astack of layers wherein at least one layer of said stack is sensitive toone of the etch compounds.

The plasma composition is preferably a Boron-halogen comprising plasmawith small additions of nitrogen.

The Boron-halogen compound is preferably BCl₃ and said small additionsof nitrogen are such that the ratio of the boron-halogen compound tonitrogen is from 19:1 up to 9:1.

Optionally an inert compound can be added to the plasma comprisingboron-halogen and nitrogen. Said inert compound can be e.g. argon orhelium (He) and these compounds can be added to the plasma inconcentrations up to 50% of the total plasma composition. It is furtherknown that addition of inert compounds (meaning that these compounds donot react with the substrate to be etched such that volatile compoundsare formed) can improve the dissociation rate in the plasma and henceimprove the etch rate and more specifically in case of the inventionimprove the formation (deposition) of a BxNy film. In that case theinert compound can be seen as a catalyst.

For the patterning of metal gates comprising TaN, such as TaN metalgates and metal gates comprising layers of TaN and TiN (TaN/TiN metalgates) the ratio of the boron-halogen compound to nitrogen is below 9:1(having more boron-halogen), more preferred said ratio of theboron-halogen compound to nitrogen is below 11:1 and most preferred saidratio of the boron-halogen compound to nitrogen is 19:1.

For the patterning of metal gates comprising TaN, such as TaN metalgates and metal gates comprising combinations of TaN and TiN layers(TaN/TiN metal gates) the ratio of BCl₃ to nitrogen is below 9:1, morepreferred said ratio of BCl₃ to nitrogen is below 11:1 and mostpreferred said ratio of BCl₃ to nitrogen is 19:1.

For the patterning of germanium comprising stacks wherein germanium isat least one of the layers of the stack and said germanium layer needsto be protected to avoid lateral attack during patterning of a layersituated under said germanium layer, the ratio of the boron-halogencompound to nitrogen is higher than 19:1. More preferred said ratio ofthe boron-halogen compound to nitrogen is higher than 11:1 and mostpreferred the ratio of the boron-halogen compound to nitrogen is 9:1.

For the patterning of germanium comprising stacks wherein germanium isat least one of the layers of the stack said germanium layer needs to beprotected to avoid lateral attack during patterning of a layer situatedunder said germanium layer, the ratio of BCl₃ to nitrogen is higher than19:1. More preferred said ratio of BCl₃ to nitrogen is higher than 11:1and most preferred the ratio of BCl₃ to nitrogen is 9:1.

In a preferred embodiment, the plasma composition is preferably a plasmacomprising (or consisting of) a Boron-halogen compound and nitrogen, orin other words small additions of nitrogen in a boron-halogen plasma.

Preferably, the plasma comprises (or consists of) a boron-halogencompound and 5% up to 10% nitrogen (of the total plasma composition).

More preferred, the plasma composition comprises (or consists of) aboron-halogen compound and less than 10% nitrogen (of the total plasmacomposition) and most preferred said boron-halogen is BCl₃.

For the patterning of germanium comprising stacks wherein said germaniumlayer needs to be protected to avoid lateral attack during patterning ofa layer situated under said germanium layer, the amount of N₂ to thetotal BCl₃/N₂ plasma composition is higher than 5%, more preferred saidamount of N₂ is higher than 8% N₂ to the total BCl₃/N₂ plasmacomposition and most preferred said amount of N₂ is 10% to the totalBCl₃/N₂ plasma composition.

For the patterning of metal gates such as TaN and/or combinations of TaNand TiN (TaN/TiN metal gates) the amount of N₂ to the total BCl₃/N₂plasma composition is lower than 10%, more preferred said amount of N₂is lower than 8% N₂ to the total BCl₃/N₂ plasma composition and mostpreferred said amount of N₂ is 5% to the total BCl₃/N₂ plasmacomposition.

Preferably the plasma of the preferred embodiments (during patterning)has a substrate bias which is different from zero.

Preferably the plasma of the preferred embodiments (during patterning)has a plasma power is from 100 W up to 1200 W. More preferred saidplasma power is about 450 W.

Preferably the plasma of the preferred embodiments (during patterning)has a pressure in the plasma chamber of minimum 0.666 Pa (5 mT) andmaximum 10.665 Pa (80 mT). More preferred said pressure is 0.666 Pa (5mT).

Preferably the plasma of the preferred embodiments (during patterning)has a temperature below 100° C. and most preferred said plasmatemperature during dry-etch patterning is about 60° C. A boron-nitrogen(B_(x)N_(y) or BN) film deposited at higher temperatures is equal to ahigher quality film containing less (or no) impurities which is moredifficult or even not possible to remove.

A method is provided for the dry etching of non-Si comprising gatestacks, said non-Si comprising gate stacks are preferably metal gatecomprising gate stacks such as TaN comprising gate stacks and preferablymetal gate stacks comprising a (pure) germanium layer.

More specifically the dry-etching method of the preferred embodimentsuses a plasma composition wherein at least one layer of said stack istoo sensitive to one of the etch compounds.

Said dry etching method is characterized in that the vertical profile ofsaid gate stack is preserved after etching. The method of the preferredembodiments solves or minimizes the problem of negatively sloped gateprofiles after dry etching by depositing a sacrificial layer during theetching. Said sacrificial layer serves as a passivating layer during dryetching such that the vertical profile or CD of the gate stack ispreserved.

The dry-etching method of the preferred embodiments solves or minimizesthe problem of lateral etch and profile attack during the patterning ofadvanced gate stacks such as metal gate stacks and germanium comprisingstacks by adding small amounts of nitrogen to a boron-halogen plasmasuch as BCl₃ plasma in order to improve gate profile control. Themixture of BCl₃/N₂ plasma results in a deposition of BxNy-like film thatinhibits the lateral etch but does not inhibit vertical etch as theformed BxNy-like film is destroyed by ion bombardment.

Preferably the method of the preferred embodiments comprises the stepsof first applying a dry-etch step using the plasma composition of thepreferred embodiments whereby during the etching a protective andwater-soluble film is deposited onto the vertical sidewalls of saidstructure such that the vertical profile of said structure is preservedand lateral attack is avoided. In a next step said water-soluble film isremoved from said structure.

Said water-soluble film is preferably removed using a wet removalprocess, most preferred said wet removal is using water.

The dry-etching method of the preferred embodiments uses a boron-halogencomprising plasma with small additions of nitrogen.

The Boron-halogen compound is preferably BCl₃ and said small additionsof nitrogen are such that the ratio of the boron-halogen compound tonitrogen is from 19:1 up to 9:1.

Optionally an inert compound can be added to the plasma comprisingboron-halogen and nitrogen. Said inert compound can be e.g. argon orhelium (He) and these compounds can be added to the plasma inconcentrations up to 50% of the total plasma composition.

In a method of the preferred embodiments for patterning metal gates suchas TaN metal gates and metal gates comprising combinations of TaN andTiN (TaN/TiN metal gates), the ratio of the boron-halogen compound tonitrogen is preferably below 9:1. More preferably, said ratio of theboron-halogen compound to nitrogen is below 11:1 and most preferred saidratio of the boron-halogen compound to nitrogen is 19:1.

In particular, said boron-halogen compound is BCl₃.

In a method of the preferred embodiments for patterning germaniumcomprising stacks, wherein said germanium layer is a layer of the stackwhich needs to be protected to avoid lateral attack during patterning ofa layer situated under said germanium layer, the ratio of theboron-halogen compound to nitrogen is preferably higher than 19:1. Morepreferred said ratio of the boron-halogen compound to nitrogen is higherthan 11:1 and most preferred the ratio of the boron-halogen compound tonitrogen is 9:1.

In particular, said boron-halogen compound is BCl₃.

In a preferred embodiment, the plasma composition used in a method ofthe preferred embodiments is a plasma comprising (or consisting of) aBoron-halogen compound and nitrogen, or in other words small additionsof nitrogen in a boron-halogen plasma.

Preferably, the plasma comprises (or consists of) a boron-halogencompound and 5% up to 10% nitrogen (of the total plasma composition).

More preferred, the plasma composition comprises (or consists of) aboron-halogen compound and less than 10% nitrogen (of the total plasmacomposition) and most preferred said boron-halogen is BCl₃.

In a method of the preferred embodiments for patterning germaniumcomprising stacks wherein said germanium layer needs to be protected toavoid lateral attack during patterning of a layer situated under saidgermanium layer, the amount of N₂ to the total BCl₃/N₂ plasmacomposition is higher than 5%, more preferred said amount of N₂ ishigher than 8% N₂ to the total BCl₃/N₂ plasma composition and mostpreferred said amount of N₂ is 10% to the total BCl₃/N₂ plasmacomposition.

In a method of the preferred embodiments for patterning metal gates suchas TaN and/or combinations of TaN and TiN (TaN/TiN metal gates), theamount of N₂ to the total BCl₃/N₂ plasma composition is lower than 10%,more preferred said amount of N₂ is lower than 8% N₂ to the totalBCl₃/N₂ plasma composition and most preferred said amount of N₂ is 5% tothe total BCl₃/N₂ plasma composition.

Preferably the plasma used in a method of the preferred embodiments(during patterning) has a substrate bias which is different from zero.

Preferably, said plasma has a plasma power of 100 W up to 1200 W. Morepreferred said plasma power is about 450 W.

Preferably, said plasma has a pressure in the plasma chamber of minimum0.666 Pa (5 mT) and maximum 10.665 Pa (80 mT). More preferred saidpressure is 0.666 Pa (5 mT).

Preferably, said plasma has a temperature below 100° C. and morepreferred said plasma temperature during dry-etch patterning is about60° C.

Indeed, a boron-nitrogen (B_(x)N_(y) or BN) film deposited at highertemperatures is equal to a higher quality film containing less (or no)impurities, which is more difficult or even not possible to remove.

In relation to the drawings the preferred embodiments can also bedescribed as follows in the text below.

A method is provided for the dry etching of non-Si comprising gatestacks, said non-Si comprising gate stacks are preferably metal gatecomprising gate stacks such as TaN comprising gate stacks and preferablypure germanium comprising metal stacks. Said dry etching method ischaracterized in that the vertical profile of said gate stack ispreserved after etching. The method of the preferred embodiments solvesthe problem of negatively sloped gate profiles after dry etching bydepositing a sacrificial layer during the etching. Said sacrificiallayer serves as a passivating layer during dry etching such that thevertical profile or CD of the gate stack is preserved.

A composition is provided of a plasma used to etch materials that aretoo sensitive to Cl-based plasmas. If those materials are etched withpure Cl-based plasmas such as BCl₃ plasmas, the etch profiles aredistorted because these materials are etched in the lateral direction aswell. Examples of said materials are metal gate comprising gate stackssuch as TaN comprising gate stacks and pure germanium comprising metalstacks. The plasma of the preferred embodiments solves or minimizes theproblem of damage caused by Cl-based plasmas, more specifically this isachieved by adding small amounts of nitrogen to the Cl-based plasma. Forthe patterning of metal gate comprising gate stacks such as TaNcomprising gate stacks and pure germanium comprising metal stacks saidCl compound is preferably BCl₃. The amount of nitrogen added to theplasma is preferably from 5% up to 10%. The addition of nitrogen to aCl-based plasma such as BCl₃ preserves the vertical profile through theformation of a passivating B_(x)N_(y)-like layer on the verticalsurfaces.

A Cl-based plasma with small additions of nitrogen for the patterning ofnon-Si based stacks is also provided. Said patterning is furthercharacterized as a patterning which avoids lateral etching and preservesthe vertical profile. Said stacks are preferably metal gate comprisinggate stacks such as TaN comprising gate stacks and preferably puregermanium comprising metal stacks. For patterning TaN comprising gatestacks and pure Germanium comprising gate stacks, said Cl compound isBCl₃.

EXAMPLES

The method of the preferred embodiments as well as the plasma and itsuse can be applied to any material that can be etched by Cl-based plasmabut is too chemically reactive and has significant lateral etchcomponent. Said lateral etch can be blocked by a BxNy-like passivationfilm deposited onto the vertical sidewalls while at the meanwhile thevertical etch is not significantly affected.

The BCl₃/N₂ plasma was applied for patterning of two different stacks asdescribed in Example 1 and 2: pure Ge gates and TaN metal gates in theTiN/TaN gate stack. In both cases, the lateral attack of the gatematerial was prevented by addition of small amount of N₂ (5%-10%) to theBCl₃ plasma. Furthermore the plasma settings were optimized andillustrated in Example 3. The deposited (passivation) BxNy-like layer ofthe preferred embodiments is characterized by FTIR and illustrated inExample 4.

Example 1 Application of BCl₃/N₂ Plasma for TaN Gate Profile Control

The BCl₃/N₂ plasma was used to etch TaN metal gates, in the examplepresented here said TaN metal gate is present in a TiN/TaN gate stackwhere 15 nm TaN is in the contact with the gate dielectric and 70 nm TiNcovers the TaN or in other words 70 nm TiN is situated on top of said 15nm TaN.

The most critical step is TaN etching after TiN patterning. BCl₃ plasmais used here for the TaN patterning as it is selective to the Sisubstrate and can be used as high-k removal as well.

If TaN is etched with pure BCl₃ plasma, then a notch (lateral attack) isobserved in the TaN layer.

FIG. 4A shows the gate profile after etching in pure BCl₃, an arrowindicates the lateral attack of TaN.

The addition of 5% of N₂ to the BCl₃ plasma resulted in a straight TaNprofile without the lateral attack of the TaN layer.

The effect of N₂ addition is illustrated in FIG. 4B. A B_(x)N_(y)comprising passivation layer will be deposited onto the verticalsidewalls of the stack during patterning, said B_(x)N_(y) comprisingpassivation layer will protect the TaN during patterning and avoidlateral attack.

The deposition of a B_(x)N_(y) comprising layer onto the horizontalsurfaces will be negligible due to a continuous ion bombardment in thevertical direction (in other words the B_(x)N_(y) comprising layer willbe removed immediately after deposition onto horizontal surfaces).

This means that the deposition of the BxNy like film inhibits thelateral etch but does not inhibit vertical etch as the formed BxNy-likefilm is destroyed by ion bombardment.

A straight TaN profile can also be obtained by using a BCl₃/O₂ plasmamixture, as shown in FIG. 5B. However, the presence of O₂ in the etchingplasma will have a detrimental effect on the high-k dielectric and,therefore, is preferably avoided.

After patterning of the TaN comprising gate stack, the B_(x)N_(y)comprising passivation layer can be removed by a wet treatment e.g. aremoval in water.

Example 2 Application of BCl₃/N₂ Plasma for Pure Ge Gate Profile Control

The BCl₃/N₂ plasma was used to pattern pure Ge gates having a high-kdielectric underneath (in the presented case the high-k dielectric isHfO₂). The high-k dielectric must be removed selectively to theunderlying Si substrate.

The Ge gate profile just after patterning and before high-k removal asshown in FIG. 2 is straight.

The conventional way of HfO₂ removal is etching in BCl₃ plasma. Ifhigh-k is removed by such plasma, the Ge gate suffers from profiledistortion while addition of 10% N₂ to the BCl₃ plasma preserves theprofile even if the removal time is doubled as shown in FIG. 3.

FIG. 3A shows the Ge gate profile after high-k removal by a pure BCl₃plasma for 10 seconds and FIG. 3B shows the Ge gate profile after high-kremoval by a BCl₃/N₂ (10% N₂) plasma for 20 seconds. No lateral attackof the Ge profile is seen in FIG. 3B.

It can be concluded that addition of small amounts of N₂ (in thepresented case 10% N₂ was added) to the BCl₃ plasma during high-kremoval preserves the shape of the Ge gate. This is due to thedeposition of a BxNy-like passivation film on the gate (vertical)sidewalls. Said BxNy-like passivation film is a sacrificial layer whichcan be removed afterwards by wet treatment.

Example 3 Plasma Parameters Used to Deposit a BxNy Passivation Film

The plasma parameters used for the deposition of a BxNy passivation filmduring TaN metal gate patterning as presented in Example 1 using aplasma of a preferred embodiment are as follows: pressure 0.666 Pa (5mT), plasma power 450 W, flow BCl₃ 95 sccm (standard centimeter cube perminute), flow N₂ 5 sccm, and substrate bias 55V.

The plasma parameters used for the deposition of a BxNy passivation filmduring high-k removal in a Ge gate stacks as presented in Example 2 areas follows: pressure 0.666 Pa (5 mT), plasma power 450 W, substrate bias30V, BCl₃ 90 sccm, N₂ 10 sccm.

Example 4 Characterization of the Deposited BxNy Layer

Using the plasma composition (BCl₃/N₂) and method of the preferredembodiments resulted in the deposition of a BxNy layer. Said BxNy filmwas characterized by Fourier Transmission Infra-Red spectrometry (FTIR)and X-ray Photoelectron Spectroscopy (XPS). It was found that a plasmamixture of BCl₃ and N₂ resulted in the deposition of a BxNy film onto a(flat) wafer surface if no bias was applied to the substrate (to avoidion bombardment). Said BxNy film was deposited in an etch chamber (LAMVersys 2300) at 60° C. and 275° C. at a rate as high as 300 nm/mindepending on the pressure, plasma power, gas flows and BCl₃ to N₂ ratio.

The FTIR spectra of the BxNy films deposited at 60° C. and 275° C. (forcomparison) are shown in FIG. 1. A strong peak at about 1400 cm⁻¹ isattributed to a hexagonal boron nitride (h-BN). This peak dominate thespectrum of the film deposited at 275° C. but the spectrum of the filmdeposited at 60° C. contains number of other peaks and, therefore, thatfilm is not pure BN.

The XPS analysis of the surface of the film deposited at 60° C. showedprimarily boron (about 36%), nitrogen (about 20%) and oxygen (about36%). Some carbon (about 7%) is attributed to the contamination from theatmosphere. The amount of chlorine did not exceed 1%. As the depositionplasma contains no O₂, the significant amount of oxygen in the film is asign of the film oxidation during the atmosphere exposure.

The deposited BxNy-like film was found to be easily decomposing bytemperature (the film thickness decreases at temperatures above 100° C.)and soluble in water at room temperatures. These properties makecleaning of any deposited inhibitor layer easy: the water rinse isenough to clean any BxNy-like film that is left after the gatepatterning.

It can be concluded that by mixing BCl₃ and N₂ in a plasma etch chamberit is possible to deposit a BxNy-like film that contains almost no Cl₂.The film is relatively unstable and can be easily removed by a waterrinse, as it is soluble in water.

All references cited herein are incorporated herein by reference intheir entirety. To the extent publications and patents or patentapplications incorporated by reference contradict the disclosurecontained in the specification, the specification is intended tosupersede and/or take precedence over any such contradictory material.

The term “comprising” as used herein is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps.

All numbers expressing quantities of ingredients, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe specification and attached claims are approximations that may varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should be construed in light of the number ofsignificant digits and ordinary rounding approaches.

The above description provides several methods and materials of thepresent invention. This invention is susceptible to modifications in themethods and materials, as well as alterations in the fabrication methodsand equipment. Such modifications will become apparent to those skilledin the art from a consideration of this disclosure or practice of theinvention disclosed herein. Consequently, it is not intended that thisinvention be limited to the specific embodiments disclosed herein, butthat it cover all modifications and alternatives coming within the truescope and spirit of the invention as embodied in the attached claims.

1. A dry-etch plasma composition for preserving a vertical profile of astructure comprising a stack of layers, wherein a removablewater-soluble film is deposited onto the sidewalls of the stack from theplasma composition during dry-etch patterning of the stack, such thatlateral attack of the patterned stack is avoided.
 2. The plasmacomposition of claim 1, wherein the plasma comprises a boron-halogencompound and nitrogen.
 3. The plasma composition of claim 2, furthercomprising an inert compound.
 4. The plasma composition of claim 2,wherein a ratio of the boron-halogen compound to nitrogen is from 19:1to 9:1.
 5. The plasma composition of claim 2, wherein the boron-halogencompound is BCl₃.
 6. The plasma composition of claim 1, wherein thestack of layers is a metal gate-comprising stack.
 7. The plasmacomposition of claim 6, wherein the metal gate-comprising stackcomprises TaN or TaN/TiN.
 8. The plasma composition of claim 6, whereinat least one layer of the stack of layers is a germanium-comprisinglayer.
 9. The plasma composition of claim 8, wherein the germanium layeris situated upon a layer to be patterned by the plasma composition. 10.The plasma composition of claim 1, wherein the substrate bias isdifferent from zero.
 11. The plasma composition of claim 1, wherein theplasma power is from 100 W to 1200 W.
 12. The plasma composition ofclaim 11, wherein the plasma power is about 450 W.
 13. The plasmacomposition of claim 1, wherein the pressure in the plasma chamber isfrom 0.666 Pa to 10.665 Pa.
 14. The plasma composition of claim 1,wherein the pressure in the plasma chamber is 0.666 Pa.
 15. The plasmacomposition of claim 1, wherein a temperature of the plasma duringpatterning is below 100° C.
 16. The plasma composition of claim 1,wherein a temperature of the plasma during patterning is about 60° C.17. The plasma composition of claim 1, wherein the plasma consists of aboron-halogen compound and nitrogen, and wherein from 5% to 10% of thetotal plasma composition is nitrogen.
 18. The plasma composition ofclaim 1, wherein the plasma consists of a boron-halogen compound andnitrogen, and wherein less than 10% of the total plasma composition isnitrogen.
 19. The plasma composition of claim 1, wherein the plasmaconsists of a boron-halogen compound and nitrogen, and wherein less than8% of the total plasma composition is nitrogen.
 20. The plasmacomposition of claim 1, wherein the plasma is a BCl₃ plasma wherein 5%of the total plasma composition is nitrogen.
 21. An anisotropical dryetching method for patterning a stack of layers to create a verticalstructure, the method comprising the steps of: patterning a stack oflayers to create a vertical structure by dry etching using a plasmacomposition comprising a boron-halogen compound and nitrogen, wherein aprotective and water-soluble film is deposited from the plasma ontovertical sidewalls of the structure during dry etching, such that avertical profile of the structure is preserved and lateral attack isavoided during dry etching; and removing the film from the structure.22. The method of claim 21, wherein the film is removed by a wet removalprocess using water.
 23. The method of claim 21, wherein a ratio ofboron-halogen compound to nitrogen is from 19:1 to 9:1.
 24. The methodof claim 21, wherein the boron-halogen compound is BCl₃.
 25. The methodof claim 21, wherein the plasma further comprises an inert compound. 26.The method of claim 21, wherein the stack of layers is a metalgate-comprising stack.
 27. The method of claim 26, wherein the metalgate-comprising stack comprises TaN or TaN/TiN.
 28. The method of claim26, wherein at least one layer of the stack of layers comprisesgermanium.
 29. The method of claim 28 wherein the germanium-comprisinglayer is situated upon a layer to be patterned by the plasmacomposition.
 30. The method of claim 21, wherein a substrate bias duringpatterning is different from zero.
 31. The method of claim 21, wherein aplasma power during patterning is from 100 W to 1200 W.
 32. The methodof claim 21, wherein a plasma power during patterning is about 450 W.33. The method of claim 21, wherein a pressure in the plasma chamberduring patterning is from 0.666 Pa to 10.665 Pa.
 34. The method of claim21, wherein a pressure in the plasma chamber during patterning is 0.666Pa.
 35. The method of claim 21, wherein the temperature of the plasmaduring patterning is below 100° C.
 36. The method of claim 21, whereinthe temperature of the plasma during patterning is about 60° C.
 37. Themethod of claim 21, wherein the plasma consists of a boron-halogencompound and nitrogen, and wherein from 5% to 10% of the total plasmacomposition is nitrogen.
 38. The method of claim 21, wherein the plasmaconsists of a boron-halogen compound and nitrogen, and wherein less than10% of the total plasma composition is nitrogen.
 39. The method of aclaim 21, wherein the plasma consists of a boron-halogen compound andnitrogen, and wherein less than 8% of the total plasma composition isnitrogen.
 40. The method of claim 21, wherein the plasma is a BCl₃plasma wherein 5% of the total plasma composition is nitrogen.